A security flaw in Netscape's SmartDownload browser plug-in leaves users vulnerable to attack even if the application is disabled.

The simple act of visiting a Web site with a maliciously constructed URL could be enough for a Trojan horse program to infect the user's Windows PC, BugTraq claims. A buffer overflow bug in the SmartDownload library (called sdph20.dll) can allow an attacker to execute arbitrary code on an infected machine. The problem is compounded by the fact SmartDownload analyses a URL whether or not it is enabled, so disabling the application will have no effect. Buffer overflows are a common class of security vulnerability, connected with sloppy programming, which can allow malicious code, contained at the end of an input much longer than a program is set up to take, to be injected into a system. In this case, postings on BugTraq suggest a (so far theoretical) exploit could use this vunerablity to insert a backdoor program on a victim's machine. A Web page could be created without even crashing the browser. The vulnerability is patched with version 1.4 of SmartDownload but according to software developers site Betanews, Netscape has failed to warn users that they need to upgrade. AOL Operations Security (OpsSec) warned in an urgent e-mail on Friday, Betanews reports, "that all vulnerable systems immediately upgrade to Netscape SmartDownload v1.4 'or' completely uninstall/remove SmartDownload v1.3." Confusingly, a link from the BugTraq posting on the problem, which was first publicised by security researchers @stake, points to a location where the latest version of SmartDownload might be obtained. Despite this, and as BetaNews correctly points out, the Netscape site contains no reference to SmartDownload v1.4. SmartDownload adds pause, resume and auto-restart download capabilities to common Web browsers. It is installed by default with the latest versions of Netscape Communicator (and also work with Internet Explorer).